There is a desire in the industry for higher circuit density in microelectronic devices made using lithographic techniques. One method of achieving higher area density is to improve resolution of circuit patterns in resist films. The use of shorter wavelength radiation (e.g. deep UV-220 to 280 nm) than the currently employed near and mid-UV spectral range (300 nm to 450 nm) offers the potential for improved resolution. However, with deep UV radiation, fewer photons are transferred for the same energy dose to achieve the same photochemical response. Further, current lithographic tools have greatly attenuated output in the deep UV spectral region. Therefore, there is a need in the art to develop resist materials which are more sensitive to radiation in deep UV.
Polysilanes are known in the art for use as a resist e.g. in making a bilayer photoresist. The bilayer resist comprises an imaging oxygen plasma resistant polysilane layer over a planarizing polymer layer coated on a substrate. When the resist is imaged, the radiation causes photochemical degradation of the exposed polysilane into lower molecular weight materials. Photochemical degradation is accompanied by a proportional amount of spectral bleaching which is used in the art to measure the degree of degradation. Degradation of the exposed polysilane enables wet development of a positive image with common organic solvents. The image is then transferred through the underlying polymer layer to the substrate by oxygen plasma development. However, current polysilanes lack sensitivity and require large radiation doses of 100 to 400 millijoules/cm.sup.2 for suitable imaging and therefore are generally less desirable for commercial use especially in deep UV.
Polysilane polymers have been sensitized towards photodecomposition by incorporating certain agents into the polymer. Miller et al., Materials for Microlithography ACS Symposium Series 266, page 293, 1984, discloses incorporating 1,4-bis(trichloromethyl)benzene or 1,3,5-tris (trichloromethyl)triazine into polysilane to increase the rate of spectral bleaching upon irradiation. However, there is a desire in the electronics industry to avoid the use of chlorinated materials in resist compositions.
Freedman et al. in U.S. Pat. No. 3,932,352 issued Jan. 13, 1976, discloses the use of N-halosuccinimide to enhance photodegradation of plastic material such as polyolefin film. However, it is preferred in the industry to avoid halogenated materials in resist compositions. It is therefore an object of the present invention to provide improved photosensitizers for polysilane resist compositions.
Other objects and advantages will become apparent from the following disclosure.